Fuel pump

ABSTRACT

A fuel pump for an engine may include a cylinder, a piston displaceably disposed in the cylinder, and a cam driven by the engine. The cam engages the piston to form a cam-follower mechanism so that the rotation of the cam generates a reciprocal movement of the piston inside the cylinder. The cam preferably includes a variable cam lobe having a maximum radius that is a function of engine speed so that the displacement of the piston generated by the variable cam lobe is a function of the engine speed. The cam may also include a weight that is subject to a centrifugal force when the ram is rotating. Alternatively, the maximum radius of the variable cam lobe may be a function of pump outlet pressure so that the displacement of the piston generated by the variable cam lobe is a function of the pump outlet pressure.

FIELD OF THE INVENTION

[0001] The present invention relates to a fuel pump, in particular to afuel pump having a variable displacement.

BACKGROUND OF THE INVENTION

[0002] One of the problems associated with conventional fuel pumps isthat they cannot rapidly pressurize the fuel system during both verycold (−20 to −40° F.) and hot-soak restart conditions, unless they aredrastically oversized with respect to all other operating conditions.The cause of this phenomenon is that the fuel pumps are inefficient at alow pump speeds, such as below 90 RPM. The efficiency of the fuel pumpsis about 30% at low speed but is more than 90% at a high speed. Sincemost conventional fuel pumps are driven by engine cam-shafts and areoperating at one half of the engine speed, they frequently operate inthe low-efficiency range. Typically, the worst condition is encounteredat cold startup temperatures, which can cause the engine idle speed todrop as low as 80 RPM and the pump speed to 40 RPM.

[0003] The problem is especially profound with respect to directinjection spark ignition engines. The advantages of the direct injectionspark ignition are lower cold start hydrocarbons and better engine starttimes resulting from better fuel preparation. Thus the fuel preparationsystem must operate properly during startup conditions to achieve theseadvantages. The high pressure fuel injectors, which are better thantoday's PFI fuel injectors from a fuel atomization standpoint, depend onhigher fuel pressures to provide the level of atomization needed toproduce better cold start results.

SUMMARY OF THE INVENTION

[0004] The present invention solves this problem of the conventionalfuel pump by providing a fuel pump with a displacement that varies withone or more engine parameters.

[0005] In accordance with one aspect of the invention, a fuel pump foran engine may include a cylinder, a piston displaceably disposed in thecylinder, and a cam driven by the engine. The cam engages the piston toform a cam-follower mechanism so that the rotation of the cam generatesa reciprocal movement of the piston inside the cylinder. The campreferably includes a variable cam lobe having a maximum radius that isa function of engine speed. As a result, the displacement of the pistongenerated by the variable cam lobe is also a function of engine speed.

[0006] A pivotable arm pivotably connects a weight to the cam and isconnected to the variable cam lobe. When the cam is rotating, the weightextends radially outwards under the centrifugal force to vary themaximum radius of the variable cam lobe. The cam may further includespring biasing the weight radially inwards to counter the centrifugalforce.

[0007] When the variable cam lobe is at the extended position, a stop,by engaging at least one of the arm, the weight and the variable camlobe, prevents the variable cam lobe from being pushed beyond theextended position by the centrifugal force.

[0008] The variable cam lobe may have only an extended position and aretracted position. When the engine speed is below a given engine speedvalue, the variable cam lobe is at the extended position, and when theengine speed is above a given engine speed value, the variable cam lobeis at the retracted position. Alternatively, the maximum radius of thevariable cam lobe may be adjusted continuously between the fullyretracted and fully extended positions.

[0009] In accordance with another aspect of the invention, a fuel pumpfor an engine may include a cylinder, a piston displaceably disposed inthe cylinder, and a cam driven by the engine. The cam engages the pistonto form a cam-follower mechanism so that the rotation of the camgenerates a reciprocal movement of the piston inside the cylinder. Thecam preferably includes a variable cam lobe having a maximum radius thatis a function of pump outlet pressure so that the displacement of thepiston generated by the variable cam lobe is a function of the pumpoutlet pressure. Preferably, the maximum radius of the variable cam lobedecreases as the pump outlet pressure increases.

[0010] When the pump outlet pressure is below a given value, thevariable cam lobe is at the extended position, and when the pump outletpressure is above the given value, the cam lobe is at the retractedposition.

[0011] The present invention has a number of advantages overconventional fuel pumps. For example, since the cam of the pump has avariable cam lobe whose maximum radius varies with engine speed or fuelpressure, the pump does not have to be oversize for high-speedoperations. As a result, energy is not wasted pumping unneeded fuel athigh-speed operations, and engine efficiency is improved. In addition,the size of the fuel pump can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a schematic drawing of an embodiment of the presentinvention having a fixed cam lobe and a variable cam lobe with thevariable cam lobe in an extended position.

[0013]FIG. 2 is a schematic drawing of the embodiment of FIG. 1 with thevariable cam lobe in a retracted position.

[0014]FIG. 3 is a schematic drawing of another embodiment of the presentinvention having two fixed cam lobe and two variable cam lobes with thevariable cam lobes in an extended position.

[0015]FIG. 4 is a schematic drawing of the embodiment of FIG. 3 with thevariable cam lobes in a retracted position.

[0016]FIG. 5 is a schematic drawing of a further embodiment of thepresent invention having a variable cam lobe, the position of which iscontrolled by fuel pressure.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0017]FIGS. 1 and 2 illustrate an embodiment of the fuel pump of thepresent invention. The fuel pump 10 shown in FIGS. 1 and 2, which may beused with an engine, such as an automotive engine, includes a cylinder20, a piston 30 disposed in the cylinder 20, and a cam 40 driven by theengine.

[0018] The cylinder 20 shown in FIGS. 1 and 2 may be connected to aninlet fuel line 22 and an outlet fuel line 24. The inlet fuel line 20includes a one-way valve 26 that allows only inflow, and the outlet fuelline 24 includes a one-way valve 28 that allows only outflow. As thepiston 30 moves upwards, the one-way valve 26 in the inlet fuel line 22opens to allow fuel to flow into the cylinder 20 from a fuel tank orfrom a primary fuel supply pump, and the one-way valve 28 in the outletfuel line 24 closes to prevent the fuel from flowing back into thecylinder 20. As the piston 30 moves downwards, the one-way valve 28 inthe outlet fuel line 24 opens to allow the fuel to be pumped to, forexample, a fuel injector, and the one-way valve 26 in the inlet fuelline 22 closes to prevent the fuel from being pumped back into the fueltank or the primary fuel supply pump.

[0019] In the embodiment shown in FIGS. 1 and 2, the piston 30 isconnected to a cam follower 32 via a piston rod 34. The cam follower 32preferably is pushed against the cam 40 by a spring (not shown) or thelike to ensure the cam follower 32 and the cam 40 are in contact. As thecam 40 rotates, the cam 40 and spring push the cam follower 32 andpiston 30 back and forth to pump fuel.

[0020] The cam 40 shown in FIGS. 1 and 2 has a fixed cam lobe 42 and avariable cam lobe 44, although a cam of the present invention mayinclude more than one variable cam lobe and may have no fixed cam lobe.Each cam lobe has a maximum radius, which is defined as the point on thecam lobe which is farthest from the cam's center of rotation. In certaincases, the maximum radius of the cam lobe corresponds to the position ofthe piston at an end of its stroke. The maximum radius of a fixed camlobe is constant, while the variable cam lobe can extend and retract tochange its maximum radius. Preferably, the variable cam lobe 44 shown inFIGS. 1 and 2 has only two positions, i.e., fully retracted and fullyextended positions, although in some other embodiments the maximumradius of the variable cam lobe may be adjusted continuously between thefully retracted and fully extended positions.

[0021] The cam 40 shown in FIGS. 1 and 2 also includes a weight 46 thatis connected to the variable cam lobe 44 by an arm 48 that is pivotablyconnected to the cam 40. As the arm 48 pivots, the variable cam lobe 44moves between the retracted position, as shown in FIG. 2, and theextended position, as shown in FIG. 1. The weight 46 generates acentrifugal force when it rotates with the cam 40, and the centrifugalforce tends to pivot the arm 48 to push the variable cam lobe 44 towardsthe retracted position.

[0022] The cam 40 shown in FIGS. 1 and 2 also includes a spring 50, andthe spring 50 biases the variable cam lope 44 towards the extendedposition. In other words, the spring force tends to push the variablecam lobe 44 towards the fully extended position. In the embodiment shownin FIGS. 1 and 2, this means that the spring 50 is in tension, althoughthe spring 50 may be placed in a position so that it is compressed.Preferably, the spring 50 has a pretension when the variable cam lobe 44is at the fully extended position. The pretension of the spring 50 maybe selected so that when the centrifugal force is below a given value(or when the engine speed is below a given value), the pretension of thespring 50 is able to overcome the centrifugal force and keep thevariable cam lobe 44 in the extended position. When the centrifugalforce exceeds the given value (or when the engine speed exceeds thegiven value), the centrifugal force is able to overcome the spring forceand push the variable cam lope 44 into the fully retract position.Alternatively, the weight 46 and the characteristics of the spring 50can be selected so that the position of the variable cam lobe 44 can beadjusted continuously between the fully retracted and fully extendedpositions.

[0023] In the embodiment shown in FIGS. 1 and 2, the cam 40 may alsohave a stop 52. Preferably, when the variable cam lope 44 is at theextended position, one of the variable cam lope 44, arm 48 and weight 46rests against the stop 52 to prevent the variable cam lope 44 from beingpulled beyond the extended position by the spring 50. Additionally, thecam 40 may have another stop 54 that prevents the variable cam lope 44from being pushed beyond the fully retracted position by the centrifugalforce.

[0024] The cam 40 may be driven by the engine crankshaft or, in mostcases, by the engine camshaft, which rotates at one half of thecrankshaft speed.

[0025] In operation, during the startup phase or when engine speed islow, the centrifugal force generated by the weight 46 is not able toovercome the pretension of the spring, 50, and the variable cam lope 44is in the extended position, as shown in FIG. 1. Therefore, for everyrotation of the cam 40, the fixed and variable cam lopes 42, 44 displacethe piston 30 twice to pump fuel. When the engine speed exceeds a presetthreshold, the centrifugal force generated by the weight 46 is able toovercome the pretension of the spring 50, and the variable cam lope 44is placed in the retracted position, as shown in FIG. 2. Therefore, forevery rotation of the cam 40, only the fixed cam lope 42 displaces thepiston 30 to pump fuel. In other words, the displacement (i.e. thecapacity) of the fuel pump 10 is reduced at high engine speed.

[0026] The difference between the different pump displacements at highand low engine speeds is determined by the difference between themaximum radii of the fixed and variable cam lobes 42, 44. Therefore,this difference between the different pump displacements can be adjustedby selecting the maximum radii of the fixed and variable cam lobes 42,44.

[0027]FIGS. 3 and 4 illustrate another embodiment of the fuel pump ofthe present invention. The fuel pump 110 shown in FIGS. 3 and 4 alsoincludes a cylinder 20, a piston 30 disposed in the cylinder 20, and acam 140.

[0028] The cylinder 20 and piston 30 are identical to those shown inFIGS. 1 and 2 and therefore will be not described in connection withthis embodiment.

[0029] The cam 140 shown in FIGS. 3 and 4 has two fixed cam lobes 142and two variable cam lobes 144. The variable cam lobes 144 may have onlytwo positions, i.e., fully retracted and fully extended positions, orthey may be adjusted continuously between the fully retracted and fullyextended positions.

[0030] The positions of the variable cam lobes 144 are adjusted byrotating a second cam 156. The second cam 156 has a slotted arm 158 anda pin 160, which is attached to a pivotable arm 148 and is slideablydisposed in the slot 162 of the slotted arm 158. The pivotable arm 148is attached to a weight 146. As the pivotable arm 148 pivots, the pin160 slides in the slot 162 of the slotted arm 158 and rotates the secondcam 156. As the cam 140 rotates, the weight 146 generates a centrifugalforce, and the centrifugal force tends to pivot the pivotable arm 148 toretract the variable cam lobes 144.

[0031] The cam 140 shown in FIGS. 3 and 4 also includes a spring 150,and the spring force acts against the centrifugal force of the weight146 to pivot the pivotable arm 148 to extend the variable cam lobes 144.Preferably, the spring 150 has a pretension when the variable cam lobes144 are at the fully extended position. The pretension of the spring 150may be selected so that when the centrifugal force is below a givenvalue (or when the engine speed is below a given value), the pretensionof the spring 150 is able to overcome the centrifugal force and keep thevariable cam lobes 144 in the extended position. When the centrifugalforce exceeds the given value (or when the engine speed exceeds thegiven value), the centrifugal force is able to overcome the spring forceand push the variable cam lopes 144 into the fully retract position.Alternatively, the weight 146 and the characteristics of the spring 150can be selected so that the positions of the variable cam lobes 144 canbe adjusted continuously between the fully retracted and fully extendedpositions.

[0032] In the embodiment shown in FIGS. 3 and 4, the cam 140 may alsohave a stop 152 to prevent the variable cam lope 144 from being pulledbeyond the extended position by the spring 150. Additionally, the cam140 may have another stop 154 that prevents the variable cam lopes 144from being pushed beyond the fully retracted position by the centrifugalforce.

[0033]FIG. 5 illustrates a further embodiment of the fuel pump of thepresent invention. The fuel pump 210 shown in FIG. 5 includes a cylinder20, a piston 30 disposed in the cylinder 20, and a cam 240.

[0034] The cylinder 20 and piston 30 are identical to those shown inFIGS. 1 and 2 and therefore will be not described in connection withthis embodiment.

[0035] The cam 240 shown in FIG. 5 has a fixed cam lobe 242 and avariable cam lobe 244, although the cam may include more than onevariable cam lobe and may have no fixed cam lobe. The variable cam lobe244 shown in FIG. 5 may only two positions, i.e., fully retracted andfully extended positions, although the maximum radius of the variablecam lobe 244 may be adjusted continuously between the fully retractedand fully extended positions.

[0036] The cam 240 shown in FIG. 5 includes a piston 264 connected tothe variable cam lobe 244 by a piston rod 266. The piston 264 isslidably disposed in the cam 240. One side of the piston 264, such asthe radially outward side 268 of the piston 264 as shown in FIG. 5, isin fluid communication with the pressurized fuel output from the pump210. This can be carried out by, for example, connecting this side ofthe piston 264 with the fuel outlet 24 of the pump 210. On the otherside of the piston, such as the radially inward side 270 of the piston264, a spring 272 pushes the piston 264 radially outwards against theforce generated by the pressurized fuel.

[0037] In operation, when the fuel pressure is too low, for example whenthe engine is in the startup phase or when the engine speed is low, thespring force is able to overcome the force generated by the pressurizedfuel to push the variable cam lobe 244 radially outwards to the extendedposition. On the other hand, when the fuel pressure is within theoperating range, the force generated by the pressurized fuel is able toovercome the spring force to push the variable cam lobe 244 radiallyinwards to the retracted position.

1. A fuel pump for an engine, the fuel pump comprising: a cylinder; apiston displaceably disposed in the cylinder; and a cam driven by theengine, the cam engaging the piston to form a cam-follower mechanism sothat the rotation of the cam generates a reciprocal movement of thepiston inside the cylinder, the cam including a variable cam lobe havinga maximum radius that is a function of engine speed so that thedisplacement of the piston generated by the variable cam lobe is afunction of the engine speed.
 2. The fuel pump of claim 1, furthercomprising: a weight that is subject to a centrifugal force when the ramis rotating; a pivotable arm that pivotably connects the weight to thecam and is connected to the variable cam lobe, so that the weightextends radially outwards under the centrifugal force to vary themaximum radius of the variable cam lobe.
 3. The fuel pump of claim 2,further comprising: a spring biasing the weight radially inwards tocounter the centrifugal force.
 4. The fuel pump of claim 2, furthercomprising: a stop for engaging at least one of the arm, the weight andthe variable cam lobe when the variable cam lobe is at the extendedposition, wherein the stop maintains the variable cam lobe at theextended position.
 5. The fuel pump of claim 2, wherein the variable camlobe has only an extended position and a retracted position, whereinwhen the engine speed is below a given engine speed value the variablecam lobe is at the extended position, and wherein when the engine speedis above a given engine speed value the variable cam lobe is at theretracted position.
 6. The fuel pump of claim 1, wherein the variablecam lobe has only an extended position and a retracted position, whereinwhen the engine speed is below a given engine speed value the variablecam lobe is at the extended position, and wherein when the engine speedis above the given engine speed value the variable cam lobe is at theretracted position.
 7. The fuel pump of claim 2, wherein the variablecam lobe is a first cam lobe, and the pump further comprising a secondcam lope, wherein the second cam lope has a fixed maximum radius.
 8. Thefuel pump of claim 1, wherein the variable cam lobe is a first cam lobe,and the pump further comprising a second cam lope, wherein the secondcam lope has a fixed maximum radius.
 9. A fuel pump for an engine, thefuel pump comprising: a cylinder having an inlet and an outlet; a pistondisplaceably disposed in the cylinder; and a cam driven by the engine,the cam engaging the piston to form a cam-follower mechanism so that therotation of the cam generates a reciprocal movement of the piston insidethe cylinder, the cam including a variable cam lobe having a maximumradius that is a function of pump outlet pressure so that thedisplacement of the piston generated by the variable cam lobe is afunction of the pump outlet pressure.
 10. The fuel pump of claim 9,wherein the maximum radius of the variable cam lobe decreases as thepump outlet pressure increases.
 11. The fuel pump of claim 10, furthercomprising: a spring biasing the variable cam lobe against the pumpoutlet pressure.
 12. The fuel pump of claim 9, wherein the variable camlobe has only an extended position and a retracted position, whereinwhen the pump outlet pressure is below a given value the variable camlobe is at the extended position, and wherein when the pump outletpressure is above the given value the variable cam lobe is at theretracted position.
 13. The fuel pump of claim 9, wherein the variablecam lobe is a first cam lobe, and the pump further comprising a secondcam lope, wherein the second cam lope has a fixed maximum radius.